Which Bt to buy?

AgrEvo expects anywhere between 1 and 1.2 million U.S. corn acres to be planted to its new StarLink Bt corn hybrids that control European corn borer (ECB), based on availability.

StarLink provides a new mode of action for the control of European corn borer. All other commercial Bt corn hybrids rely on Bt genes that attack the same place in the corn borer larva's midgut. If insects were to have a change in this binding site, they would be resistant to the Bt corn and would survive and multiply.

The StarLink technology is based on a Cry9C Bt protein, which is different from the proteins used in other Bt corn. The Cry9C protein attacks a completely different place in the insect's gut. Therefore, any corn borer larvae that have developed a resistance to other Bt corn hybrids will not be resistant to StarLink Bt corn.

In May the EPA approved registration, which requires that corn harvested from StarLink hybrids in 1998 be used in domestic animal feed and industrial non-food uses. AgrEvo has licensed the technology to Garst and Croplan for use in their 1999 hybrid lineups, and more will follow.

With one more Bt technology, your buying decision becomes all the more confusing. Candice Gardner, AgrEvo field agronomist-biotechnology, recommends you base the decision on five factors, prioritized as follows:

Buy the best Bt technology/event available that controls corn borer and meets your other insect control needs. For example, do you need control of both ECB and southwestern corn borer (SWCB)? Do you need control of other pests? StarLink controls all generations of ECB and SWCB and offers suppression of black cutworm and stalk borer.

Choose the hybrid that best fits your particular maturity zone and yield environment.

Look at other management considerations. For example, is it important to have a hybrid that is resistant to not only Bt but also a herbicide? StarLink hybrids also are LibertyLink hybrids and provide resistance to AgrEvo's Liberty herbicide.

Know the refuge rules for Bt hybrids. Growers planting StarLink Bt hybrids must plant 25% of their total corn acres to a non-Bt hybrid to reduce the possibility that insects will develop resistance. If you spray for ECB, the percentage is 40%. Refuge rules currently may be different for other Bts.

Know where the grain can be marketed. Some Bt products only can be used domestically.

Farmer tests StarLink Bt

Steven Sterling, a farmer and Garst dealer from Garden City, KS, had been holding off from trying a Bt corn hybrid because he wasn't impressed with what was on the market. "The Bt hybrids controlled corn borer, but the varieties seemed to have yield drag," he says. But when AgrEvo's StarLink Bt was approved for market in May, Sterling thought he'd give it a try. On 65 acres, or half of a circle of his center-pivot irrigator, he planted a Garst 8366 Bt/LL corn hybrid. On the other half of the pivot, he planted a conventional hybrid, Garst 8366, for comparison.Turns out the StarLink Bt hybrid yielded 10 bu./acre higher than the conventional hybrid in spite of a light year for southwestern and European corn borer and hail damage of 10 to 15%. In a year of normal pressure and no hail, Sterling figures the advantage would be 15 bu./acre. "It was great," he says. "The corn stayed healthier longer and there was virtually no damage at all from corn borer." He says that on his conventional corn acres where corn borer pressure was high, 40 to 50% of the plants fell to the ground.

As a result of his test, he plans to plant 300 of his 600 corn acres to StarLink Bt next year.